New ERP calculations on 472kHz with earth-electrode antenna in 8cm snow

With several repeatable ground wave reports on 472kHz WSPR using the earth-electrode antenna, it is time for a recalculation of my ERP based on a formula (for 500kHz) supplied some years ago by M0BMU.  The assumption (from M0BMU, that I am not at all sure is right) is that the noise floor is around 3uV/m in a 2500Hz (WSPR) bandwidth. So, based on the WSPR S/N ratio the field strength when using the earth-electrodes can be calculated.

• G3ZJO at 79km gets me at around -19dB giving my field strength around 355nV/m. 
• G3XDV at 61km he gets me around -12dB S/N giving my field strength around 810nV/m.  
• M0BMU at 69km he gets me around -30dB S/N giving a field strength around 100nV/m

ERP Calculations

• ERP using G3ZJO's results = (E*d)^2 / 49; with E = 355nV, d = 79km   ERP = 16uW
• ERP using G3XDV's results = (E*d)^2 / 49; with E = 810nV, d = 61km  ERP  = 49uW
• ERP using M0BMU's results =  (E*d)^2 / 49; with E =100nV, d = 69km  ERP = 1uW

Now, to me these figures seem far too low, so perhaps the noise level is much higher than 3uV/m. Certainly that is the case here where I have an S4- S8 noise floor due to SMPSUs and other noise sources. I think these numbers can be doubled based on ground wave losses but, even so, the figures appear to be extremely low.  My Marconi antenna is some 8dB (average) better than the earth-electrode antenna and I am sure the ERP is well above 1mW using this antenna.

Conclusions

I am totally puzzled: measuring antenna current on the Marconi I get ERPs that are an order of magnitude higher yet measured results with the earth-electrode antenna average just 8dB down on the Marconi. This suggests ERPs for the earth-electrode antenna in the low mW region, which I find much more believable.

Any thoughts please?

Is this Chinese HF radio a wind up one?

As the person who started the FT818 hare running a year or so back (my thoughts and ideas for an FT817 replacement - thanks to a little Photoshop editing!) , I'm wondering if the attached is real or also a spoof?

It purports to be a new Chinese HF radio retailing for £299. It looks very much like an IC718 with some stickers on. It was brought to my attention by Steve G1KQH who found it at
http://s3.zetaboards.com/copythat/topic/7467118/1/ but the date on this is 2011. Surely if true the radio would be on sale now? Somehow I am of the opinion this is (also) a bit of wishful thinking, but I would be delighted to be proved wrong.

A real Chinese HF radio at this sort of price is not totally out of the question: labour costs are low and there are already some very nice Chinese VHF/UHF handhelds on the market that under-cut Yaesu and Icom by around 100%. It is surely just a matter of time before an FT817 or an IC718 look-alike radio is available from one of the Chinese makers.

UPDATE 1755z: maybe this IS real. See http://www.tradekey.com/product-view/1538868-518398/Hf-Transceiver-ft-808-.html

Back on the earth-electrode antenna on 472kHz

The red dots show where the wire to my far earth rod goes - under the snow!

This afternoon I've installed a coax cable from my operating shack down to the back of the garage where I do my radio building and where I can connect to the earth-electrode antenna running down the back garden. Now I have my 472kHz transverter in the garage too so it can connect directly into the earth-electrode antenna without any matching. Even with 8cm of snow on the ground and nothing of the antenna visible above the snow line (!) this antenna is still radiating a decent signal with reports already this afternoon from G3ZJO (-22dB S/N) and G3XDV (-12dB S/N) at good range. I find it truly amazing this system works at all.

I am signing G3XBM/1 on the WSPR database to distinguish my signal from that transmitted using a Marconi where I use G3XBM.  I hope no-one minds me using this suffix for a short period, but it is very much in the interests of good research. The signal level with G3XDV at 61km is about 8dB weaker on the earth-electrode antenna than on the vertical Marconi.

ILER-40 and ILER-20 QRP SSB transceiver kits

The ILER-40 and ILER-20 are low cost, simple 4-5W QRP SSB transceivers for 40m and 20m from Spain, designed by Javier EA3GCY.  They are designed around NE602 ICs working bi-directionally to save parts.

Built on a 12 x 10cm PCB, they look easy to build.  Details are available at http://www.qsl.net/ea3gcy/ . The price is a snip at just 67.50 euros plus 10 euros shipping. It looks a very well engineered kit.

ILER-40 (and ILER-20) QRP SSB kit from EA3GCY

See http://www.eham.net/reviews/detail/10700 for a number of (very good) reviews of this kit which looks like a neat introduction to QRP SSB operation. Kits now being supplied include a small AGC sub-board. The kit does not include a microphone or case.

IC7100 price

Whilst checking the trade-in value of my Elecraft K1 transceiver with Martin Lynch yesterday (in my case for another FT817), I asked when the IC7100 was likely to be available in the UK and its likely price.  Indications are that the IC7100 is going to be here in the spring with a price tag of around £1700. This does not include the D-star option. Clearly these dates and prices are not certain. It will be considerably more expensive than the IC7000 though. That much is certain.

An IC7100 at that price is rather more than I would want to pay, but if it was to last 12 years like my current FT817 already has, it might be worth it, especially with 4m,  2m and 70cm coverage. On the other hand, a second (additional) FT817 would do all I really need at under a third of the price!

E-field probe mag-mount now built

This morning I decided that it would be better to build the E-field probe for 137kHz RX at the base of the whip directly on the mag-mount base rather than inside the vehicle and having to tune out the cable capacitance. This way,  the cable capacitance is no longer an issue. I built the E-field probe into a small plastic box and arranged it so the whole unit attaches to the mag-mount using a PL259 plug in the bottom of the unit. Radio 4 on 198kHz is an S9+ signal with the mag-mount sitting on the bedroom window-sill with around 10 inches of whip. It appears to be working well.

The present design is a poor man's PA0RDT probe but using an MPF102 and a 2N3904 rather than the better devices used in Rodolph's high IP2/3 design. I may put a tuned circuit in the FET drain to increase the gain at 137kHz and reduce the gain outside the band. I will experiment with this before going out in the car.

Currently it is snowing continuously here, so road testing the EFP and checking coverage of my QRP 137kHz CW and QRSS3/30 beacon will now have to wait until later in the week.

UPDATE: I have modified the EFP so that the FET output comes from the drain with a drain tuned circuit tuned to 137kHz. I have the source resistor not decoupled initially but will consider adding this if I need a little more overall gain as the barefoot FT817 is very deaf on 137kHz.

A mag-mount as an E-field probe for 137kHz

Next week, assuming the snow has gone, I want to drive around the local area to plot the polar pattern of my earth-electrode antenna working on 137kHz.  My 7-8W beacon transmitter can send a range of QRSS and CW messages, so I want a way of driving to different places using my FT817 fed via a preamp and measuring the S/N using Spectran whilst remaining inside the car.

Portable RX loops are fine, but these are directional and need to be set up each time a measurement is taken outside of the car.  Ideally I need an omni-directional RX antenna like an E-field probe. So, I'm looking for a way to drive to a spot, take a quick measurement from inside the car, then move on; a loop works, but when it is -2 deg C outside and the ground is icy, it is not ideal.

Either I put the electronics for an E-field probe right at the base of the mag-mount (mechanically not ideal) or I have the electronics in the car and somehow tune out the coax cable capacitance.  At the moment I am still experimenting to find an arrangement that works with good sensitivity by checking the strong Greek commercial signal just outside the 137kHz band.

Based on 472kHz results, the earth-electrode antenna behaves like a loop with loop-like directionality. I 'd expect to see the same pattern on 137kHz.

K7AGE video of his KX3 build

Randy K7AGE has done a wonderfully amusing video of him building his Elecraft KX3. I won't spoil the fun, but recommend you watch it and see how it is done.

Square trade eBay Warranties - any good?

Just looked on eBay for various amateur radio items and noticed the Albrecht AE2990 10,11,12m handheld on sale from various UK suppliers from around £150. Now also shown was an optional 3 year warranty - see http://pages.ebay.co.uk/safetycentre/buyingwithconfidence/warranties/index.html which cover failures to the device outside the manufacturer's warranty period. So, for less than £200 you can have a multimode HF handheld complete with 3 yr warranty.

Peace of mind 3yr warranty for £27 - too good to be true?

My question is this. Has anyone here bought an eBay item with one of these warranties - they seem to be widely offered - and had to make a claim?  It sounds almost too good to be true. These warranties are also available on low cost VHF/UHF handhelds as well where the warranty cost is only around £8-9, which looks remarkable value if the product fails. This is as long as the warranty is a decent one that is honoured and the small print doesn't render it worthless. They also offer a 5 day repair or replacement service.

Mixed results with WSPR-X and WSPR-15

The new version of WSPR works well with plenty of reports given and received on 472kHz with it over the last 12 hours using the 2 minute version (as before but now with a waterfall and better interface), but mixed results on the slower 15 minute slot WSPR-15 which can detect much weaker signals.

My problem is TX drift over a long 15 minute transmission. My small 10W transverter is in a tiny plastic box. When using a 2 minute transmission the PA barely gets warm so there is little heat transferred to the crystal oscillator. With the much longer TX burst the PA warms more and the crystal warms up several degrees, moving the oscillator frequency by some 10s of Hz. So, although I was able to copy signals in WSPR-15, I was not able to be detected by others overnight. There are also far fewer stations monitoring yet on WSPR-15.

The solution is to rebuild the transverter into a bigger (metal) box with (a) better heatsinking so the heat rise with a mismatch is lower, (b) a slightly more efficient PA - problem here is with weather changes the antenna match goes off optimum sometimes and the heat rises as it the PA becomes less class E, and (c) put the conversion frequency oscillator physically further away from the PA, currently it is less than 10cm.

If I fix these issues and am sure that I transmit a more stable signal in the narrower (25Hz wide) WSPR-15 slot then I have a better chance of succeeding with the more sensitive version.  With another 7-9dB S/N detection improvement, my signal could reach some of the more distant stations like TF3HZ.